Category Science

How do you explain total internal reflection?

It is, indeed. What we are seeing is merely a trick of the eye or an optical illusion.

In physics, this is referred to as total internal reflection. The complete reflection of a ray of light within a medium (say water or glass) from the surrounding surfaces back into the medium is defined as total internal reflection. If the angle of incidence is greater than a certain angle, referred to as critical angle, then total reflection occurs.

An everyday example

What we see is an example of total internal reflection, happening when a swimmer dives into the swimming pool. The picture, taken near the shallow end of the swimming pool, shows a broad bubble where the swimmer has just dived in, which would also mark the water surface. While the lower portion of her reflection distorted because of the dive, the rest of the water surface is calm and hence the remaining portion of her body and the tiled bottom of the pool can be seen in the reflection at the top of the picture.

Try to notice this is the next time you take a look at a fish tank standing beside it and bending to have your eyes below the water level.

 

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Which are the two famous impact craters on earth?

Apart from planets, stars and moons, there are several small solar system bodies such as asteroids and comets in space. These are usually speeding through space. Sometimes, a larger body such as a planet or a moon can come in their way. When this happens, these extremely fast spacebodies crash into the surface of the larger space body and create a depression called impact crater.

For an object to be able to create an impact crater, it needs to be travelling at a speed of many thousand kilometres per hour. No matter how hard or tough the surface of a planet or the moon is, when a superfast object collides with it, it will definitely leave an impact by vaporizing the area and creating enormous shockwaves through the ground, which can melt and recrystallise rock.

The size and shape of a crater depends on factors such as mass, density and velocity of the impacting object, and the geology and velocity of the impacting object, and the geology of the surface it strikes. Many planets and moons in our solar system have impact craters.

Two of the famous impact craters on Earth are:

Meteor Crater

Also known as the Barringer Crater in Arizona, the U.S., this is the first crater formed by an extraterrestrial impact to be identified. It formed nearly 50,000 years ago from a meteorite that may have been up to about 150 feet wide travelling at more than 45,000 kmph.

Vredefort crater

Situated in South Africa, this is the largest-known impact crater on Earth. It is nearly 300 km in diameter and over two billion years old. However, due to erosion over time, it is difficult to see the crater. What remains today are geological structures at its centre known as the Vredefort Dome or Vredefort impact structure.

 

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First photo of Earth from the moon

Before landing humans on our moon, one of the important points of consideration, obviously, were the landing sites. In response to this need of obtaining detailed photographs of potential Apollo landing sites, NASA’s Lunar Orbiter program was born. The plan included a series of three-axis stabilized spacecraft to be inserted into lunar orbit, with each of them comprising a main engine and four solar panels.

The first of these was the Lunar Orbiter 1, designed primarily to photograph the smooth areas of the lunar surface. For this, it was fitted with a Eastman Kodak imaging system that weighed 68 kg.

Spy turns scout

The system, which employed both wide and narrow-angle lenses, had the ability to develop exposed films, scan the images and relay them back to Earth. The Eastman Kodak camera flown on the Lunar Orbiters, in fact, had been originally developed by the National Reconnaissance Office (NRO) and used in spy satellites – a truth that was revealed only after the Cold War ended.

While imaging was the primary objective, the spacecraft was also equipped with other instruments to collect data regarding radiation intensity and micro-meteoroid impact, among others. Launched on August 10, 1966, it was placed in an Earth parking orbit before being fired towards the moon.

Stumbling blocks

During its cruise to the moon, the spacecraft experienced failure to its Canopus star tracker (probably due to stray sunlight) and overheating. The former issue was resolved by navigating with the moon as the reference, and the latter was taken care of by orienting the spacecraft at a different angle off the sun.

On August 14, Lunar Orbiter 1 was injected into an orbit around the moon and began working on its objective of photographing nine potential Apollo landing sites, seven secondary areas and some sites on the far side of the moon. It successfully completed this work by August 28, with over 200 images to boast about.

Even though some of the early high-resolution images lacked quality due to smearing, the mission was largely successful as it was able to capture images covering over 5 million sq.km. of the moon’s surface. While the wide-angle images taken by this system showed resolutions up to 0.5 km, the narrow-angle pictures were accurate up to 60-80 m.

First Earthrise

Among these photos was that of the first Earthrise, captured unintentionally. During its 16th orbit around the moon on August 23, Lunar Orbiter 1 took the first photograph of our Earth taken from the moon. The image, which was shot just before the spacecraft was about to pass behind the moon, shows the crescent of the Earth. The image data was transmitted by Lunar Orbiter 1 and received at the NASA tracking station at Robledo De Chavela near Madrid, Spain.

Lunar Orbiter 1 continued working, turning its attention away from photography and focusing instead on engineering goals from September 16. The spacecraft’s condition, however, deteriorated by October 28, forcing the ground controllers to command it to impact onto the lunar surface.

On October 29, on its 577th orbit around the moon, Lunar Orbiter 1 crashed on the moon’s far side to prevent its transmission from interfering with the Lunar Orbiters to come. By the time the Lunar Orbiter program, which consisted of five orbiters, came to an end, 99% of the moon’s surface was photographed down to a resolution of 1m!

Old and new

As for the first Earthrise photo, it proved to be a remarkable image, despite the fact that the image released then was starkly black, wide and had poor resolution. The full resolution of the image wasn’t obtained from the mission data up until 2008.

The Lunar Orbiter Image Recovery Project at NASA Ames Research Center went about their task then, obtaining original mission data from tapes and restoring it to an operational condition by combining modern electronics with 1960s era parts. The result was a beautiful high resolution image of the first Earthrise photograph, a touched up version of which has been used with this story.

 

Picture Credit : Google

What do we know about the platinum group of metals?

A group of six metals – ruthenium, rhodium, palladium, osmium, iridium, and platinum-are known as the platinum group of metals or PGM. The group is called by this name because platinum is found more than the others though all of them are very rare.

The platinum groups of metals have physical, chemical and anatomical similarities. They are dense, stable and are often recycled to have longer lives. The group has a variety of highly specialized uses.

Platinum is a silvery white metal that is more expensive than gold. It is used to make jewellery. Platinum and palladium are often used as catalysts. Iridium and rhodium are harder and have a lot of alloying applications. There are very few minerals containing the platinum group of metals, and they are found mainly in South Africa and Russia.

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Why is radium not widely used now?

No one knew of the dangers radium posed when it was produced for the first time. Radium had an aura of mystery which attracted people. Moreover, people were fascinated by how it glowed when mixed with phosphor. No wonder, industries sprang up to manufacture hundreds of consumer products containing radium.

The health hazard caused by this fascinating new element was identified only later. The harmful effects of radium such as skin burns and hair loss were observed among early experimenters. Many of them died as a result of their work.

The widespread use of radium was later halted for health and safety reasons. But, its wide use in luminescent paints continued through World War II. The soft glow of radium’s luminescence made aircraft dials, gauges and other instruments visible to their operators at night.

Radium was also an early radiation source for cancer treatment. Small radioactive seeds were implanted in tumours to kill cancerous cells. Safer and more effective radiation sources are used today.

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What do we know about the discovery of radium?

The discovery of radium is one of the most interesting stories in science. The story begins with the research of the French physicist Antoine-Henri Becquerel of the ore called pitchblende containing the element uranium. Becquerel found that pitchblende gives off radiation.

Becquerel’s discovery caused great excitement among scientists. Many physicists stopped their own research and began to study this novelty. A scientist couple Marie and Pierre Curie were especially interested in pitchblende.

Eventually, they isolated a new element that gave off more intense radiation than pitchblende itself. The Curies named this new element polonium. That was not the end. They believed that there would be at least one other element in the pitchblende.

The couple continued with their studies and in 1898, they isolated a second new element- radium. Radium gave away intense radiations and it took the Curies another four years to prepare one gram of the element. To do so, they had to sift through more than seven metric tons of pitchblende!

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